As to this thread's question, I should think a larger eye would not be necessary for improved long distance vision.

Certainly, I agree with it. But it depends on how much "long distance". If you want to increase that distance a lot, before or less you'll have to increas the eye's dimensions.

I'm not so sure that this would be the case. I can look at the Moon, without the need for a telescope, and quite clearly make out the surface detail (to an extent). I think if I wanted to be able to make out more detail of a far distant object, it is more the sensor (retina) which requires extra capability than the receiver.

Let me explain my reasoning here.

Take a Nikon D40 - 6 megapixel DSLR body and fit a Nikon 85mm f2.8 lens. With the lens set to infinity, take a shot of an object on the horizon. Now, using your computer as the processor, enlarge that object to the maximum at which it remains discernable.

Now compare that with the identical shot, taken under identical conditions with the same Nikon 85 mm f2.8 lens, but using a Nikon D3x 24.5 megapixel DSLR body.

The extent to which this shot can be enlarged with the object remaining discernable will be much greater (approx. 4 X greater), yet it is the result from the very same lens and the same processor, only the sensor has been improved.

Our eye works in much the same way as this camera with a fixed focal length lens. We make sense of a particular object within our field of vision by focusing the lens on that object and then getting the brain to concentrate on it. With an improved sensor, we would be able to distinguish more detail of that object.

The eagle has an eyeball roughly the same size as a human, yet it can see far better than a human. The reason for this is that the human retina has 6.4m cones, 200k of which are in the fovea, the eagle has approximately 32m cones, 5 times that of a human. The back of the eagle’s eyeball is flatter and the retina bigger, but the lens is not much different. The brain works in a similar way to a digital zoom on a camera. It concentrates on one area of the whole picture. If that picture has a higher resolution, it can make more sense of the detail. In effect, we ‘digitally’ zoom in on an object.

If we (and eagles) were to be able to zoom in on an object optically, in the same way as a camera zoom lens, our eye would need to be restructured since eyes have a single element lens. To enable optical zooming, like a camera lens, eyes would need a multiple moving element lenses. This would create a problem, however, in that there would be a considerable loss of field of vision.

In conclusion, our eyeball does not need to be bigger in order to see further. We can see just as far as an eagle. What it needs is an improved retina in order to be able to discern more from a small area of that sensor.

There are two factors (at least in the main, for this discussion) - resolution and sensitivity. To get more resolution you need more sensors looking at a particular field of view. There is a limit to how sensitive a receptor or photosensor can get. To get more sensitivity you need to increase the total light gathered by having as wide an aperture as possible. Astronomical telescope design has always been about trying to achieve this whilst keeping aberrations to a minimum because the amount of light arriving from distant stars is very, very small indeed. The other way to improve the light gathered is to stay "on-target" for a long time to integrate the total light gathered - a long exposure. Hubble does both of these things by having a large parabolic (at least it was supposed to be) reflector and very steady positioning with no nasty effects from the light passing through the atmosphere.

In fact I just looked up Hubble and its CCD array (image sensor) is actually only 2.5 Mpixel, which is very poor by today's standards.

lyner

There are two factors (at least in the main, for this discussion) - resolution and sensitivity. To get more resolution you need more sensors looking at a particular field of view. There is a limit to how sensitive a receptor or photosensor can get. To get more sensitivity you need to increase the total light gathered by having as wide an aperture as possible. Astronomical telescope design has always been about trying to achieve this whilst keeping aberrations to a minimum because the amount of light arriving from distant stars is very, very small indeed. The other way to improve the light gathered is to stay "on-target" for a long time to integrate the total light gathered - a long exposure. Hubble does both of these things by having a large parabolic (at least it was supposed to be) reflector and very steady positioning with no nasty effects from the light passing through the atmosphere.

In fact I just looked up Hubble and its CCD array (image sensor) is actually only 2.5 Mpixel, which is very poor by today's standards.

The field of view is also relevant.The 2.5Mpx is enough for the field of view which is required and it probably reflects the fact that the resolution is largely diffraction limited in any case; more pixels would just produce the same amount of 'blurriness' in the final picture.Getting a meaningful discussion about this sort of topic requires a totally holistic view - particularly where the Intelligent Designer is concerned. (Sorry- just kidding.)

This was taken on my Nikon D300 12.3 mp and printed (slightly cropped)to 36" x 22"

If this had been taken on a 6mp camera, it would not be possible to print to this size without the diagonal lines being out of kilter. To get a print any bigger than this, I would need a camera with more pixels to its sensor.

As to this thread's question, I should think a larger eye would not be necessary for improved long distance vision.

Certainly, I agree with it. But it depends on how much "long distance". If you want to increase that distance a lot, before or less you'll have to increas the eye's dimensions.

I'm not so sure that this would be the case. I can look at the Moon, without the need for a telescope, and quite clearly make out the surface detail (to an extent). I think if I wanted to be able to make out more detail of a far distant object, it is more the sensor (retina) which requires extra capability than the receiver.

Let me explain my reasoning here.

Take a Nikon D40 - 6 megapixel DSLR body and fit a Nikon 85mm f2.8 lens. With the lens set to infinity, take a shot of an object on the horizon. Now, using your computer as the processor, enlarge that object to the maximum at which it remains discernable.

Now compare that with the identical shot, taken under identical conditions with the same Nikon 85 mm f2.8 lens, but using a Nikon D3x 24.5 megapixel DSLR body.

The extent to which this shot can be enlarged with the object remaining discernable will be much greater (approx. 4 X greater), yet it is the result from the very same lens and the same processor, only the sensor has been improved.

Our eye works in much the same way as this camera with a fixed focal length lens. We make sense of a particular object within our field of vision by focusing the lens on that object and then getting the brain to concentrate on it. With an improved sensor, we would be able to distinguish more detail of that object.

The eagle has an eyeball roughly the same size as a human, yet it can see far better than a human. The reason for this is that the human retina has 6.4m cones, 200k of which are in the fovea, the eagle has approximately 32m cones, 5 times that of a human. The back of the eagle’s eyeball is flatter and the retina bigger, but the lens is not much different. The brain works in a similar way to a digital zoom on a camera. It concentrates on one area of the whole picture. If that picture has a higher resolution, it can make more sense of the detail. In effect, we ‘digitally’ zoom in on an object.

If we (and eagles) were to be able to zoom in on an object optically, in the same way as a camera zoom lens, our eye would need to be restructured since eyes have a single element lens. To enable optical zooming, like a camera lens, eyes would need a multiple moving element lenses. This would create a problem, however, in that there would be a considerable loss of field of vision.

In conclusion, our eyeball does not need to be bigger in order to see further. We can see just as far as an eagle. What it needs is an improved retina in order to be able to discern more from a small area of that sensor.

Ok, can you show me in which way exactly you can device a camera 85 mm to discern two 1mm spots which are 1 mm far each other, on the Moon's surface?

Not sure that this has already been mentioned, but what about exposure? Isn't this a fundamental difference between a camera/telescope and an eye, which makes comparisons rather difficult? A telescope with a camera effectively catch photons over a pre-determined time period. This is how the Hubble is able to take such breath-taking shots of space, since it can sit and "look" at the same point in space and collect the infrequent photons that arrive. The eye can't do this.

In answer to Lightarrow's question, wouldn't it be possible to discern these two 1mm spots with a camera if you could get enough magnification, if you could keep the camera and lenses still enough, and if you could have an appropriate exposure time?

lightarrow To discern 2 x 1mm points 1mm apart on the Moon's surface is rather going to the extreme. The sensor required for this, I think, would need 386,242.5 megapixels. This would mean fitting more than 10k times more cones on an eagle's retina, or 50k more times for a human. This would hardly be termed as 'being able to see a long way', this is rather into the realms of Superman! But I concede, that for such incredible vision, the eye would need to be very much bigger.

Can you make do with a telescope?

dentstudent The amount of light entering the eye (or camera) is a factor in what we can see. As you say, Hubble can keep still and gather a huge amount of light over a period of time, which we cannot. Some large format cameras of 100+ mp do require exposure times running into minutes.

lightarrow To discern 2 x 1mm points 1mm apart on the Moon's surface is rather going to the extreme. The sensor required for this, I think, would need 386,242.5 megapixels. This would mean fitting more than 10k times more cones on an eagle's retina, or 50k more times for a human. This would hardly be termed as 'being able to see a long way', this is rather into the realms of Superman!

No. Not even Superman could do it, not even a sensor with infinite pixels/cm2, because of diffraction: the resolving power d of an optical system is d = λ/2NA where NA = numerical aperture and λ = wavelength; or you can consider the angular resolution: sinθ = 1.22λ/D where D = diametre of lens' aperture. Make the computations and you'll find that you can NEVER resolve those two points in the visible range with an 85 mm lens.

In answer to Lightarrow's question, wouldn't it be possible to discern these two 1mm spots with a camera if you could get enough magnification, if you could keep the camera and lenses still enough, and if you could have an appropriate exposure time?

According to thishttp://www.bostonherald.com/news/international/general/view.bg?articleid=1081922 you can see billions of miles already. Given the age of the universe, there isn't that much further to see.A bigger eye would give, in principle, better optical resolution (ie the abillity to see two things close together as separate rather than as one blur) and also, for a giver size of retinal cell detecting the light it would alow a larger number of effective "pixels". Perhaps more usefull would be the ability to see better in low light conditions.On the other hand, as has already been pointed out, eagles see better than us, and they have smaller eyes so we could improve things without making our eyes bigger.

Does anyone know what the typical angular resolution of the eye is and how it compares to the diffraction limit?

lyner

This was taken on my Nikon D300 12.3 mp and printed (slightly cropped)to 36" x 22"

If this had been taken on a 6mp camera, it would not be possible to print to this size without the diagonal lines being out of kilter. To get a print any bigger than this, I would need a camera with more pixels to its sensor.

I don't think your camera is diffraction limited. Did you use f100 as an aperture and a field of less than one degree?Like I said, there's more to it than one simple statistic!PS Have you got some dirt on your sensor? (Top left)

I think you will find all of that a mere trifle to Superman; he can do anything!

As BC has cottoned on, I am really being hypothetical and not taking distortion into account. In practice, even over a relatively short distance atmospheric distortion would render ultra long vision pretty worthless. But, by the same token, our brain does account for and correct distortion caused by our fixed focus lens. For starters, the image projected onto the retina is upside down. Looking at an object a few cms away causes this effect:But our brain compensates for this and we see the object in a more natural way. Our brain also merges two different views to give us 3d vision.

The point I am making is that we do not need a bigger eyeball to see further. Again as BC pointed out, and as I said in a previous post, our eye can already see far distant objects. I cannot be sure of this, but I think V762 Cas (in Cassiopeia) is the furthest star from Earth visible to the naked eye. 15000 light years, I think is plenty far enough. Our eye's resolution, however, could be much improved with a sensor (retina) matching the quality of that of an eagle. Since the eagle's eyeball is the same size as a human eyeball, I see no need for a larger eyeball to improve our resolution.

It was a 'normal' photograph, as I suspected.Hubble doesn't take 'normal' photos. It looks at a very small area in the centre of the 'normal' field and those 'few' Mpixcels are placed where they are wanted. An enlargement of a Hubble picture would appear glubby because of the optics. If you magnify any telescope image beyond a limit, you always get the imperfections of the optics grinning through. More sensors in the array would achieve nothing which the normal filtering of the image would achieve.As for the original question, the ultimate limitation of 'seeing' something at a distance, boils down to Signal to Noise ratio. A large diameter is necessary and that implies a long focal length. There isn't a simple answer to this, at all.

I think you will find all of that a mere trifle to Superman; he can do anything!

As BC has cottoned on, I am really being hypothetical and not taking distortion into account. In practice, even over a relatively short distance atmospheric distortion would render ultra long vision pretty worthless. But, by the same token, our brain does account for and correct distortion caused by our fixed focus lens. For starters, the image projected onto the retina is upside down. Looking at an object a few cms away causes this effect:But our brain compensates for this and we see the object in a more natural way. Our brain also merges two different views to give us 3d vision.

The point I am making is that we do not need a bigger eyeball to see further. Again as BC pointed out, and as I said in a previous post, our eye can already see far distant objects. I cannot be sure of this, but I think V762 Cas (in Cassiopeia) is the furthest star from Earth visible to the naked eye. 15000 light years, I think is plenty far enough. Our eye's resolution, however, could be much improved with a sensor (retina) matching the quality of that of an eagle. Since the eagle's eyeball is the same size as a human eyeball, I see no need for a larger eyeball to improve our resolution.

It's not about "distorsion", but about "diffraction limit", which cannot be overcome by *any* optical instrument, however perfect it could be. It's an impossibility of the *waves* of light, not a technical imperfection of the instruments.

Ask astronomers why they don't have reproduced the optical capabilities of an eagle's eye (or more) in a telescope with the same dimensions. It's not mostly about technological limitations, but mostly because of the diffraction limit.

The Naked Scientists® and Naked Science® are registered trademarks.
Information presented on this website is the opinion of the individual contributors
and does not reflect the general views of the administrators, editors, moderators,
sponsors, Cambridge University or the public at large.